Method and high-pressure mixing apparatus with self-regenerating seal

ABSTRACT

A method for forming a self-regenerating seal in a mixing chamber of a high-pressure mixing apparatus for polymeric components suitable for providing a reactive mixture for a polymerisable resin. An annular sealing element is provided in a circular housing seat inside the mixing chamber, in a sealing zone downstream the injection holes for the polymeric components; worn and/or torn parts of the annular sealing element are automatically regenerated by the same reactive mixture delivered during operation of the mixing apparatus. A high-pressure mixing apparatus with self-regenerating sealing element is also claimed.

This U.S. Non-Provisional application is a continuation of U.S.application Ser. No. 14/178,505 filed on Feb. 12, 2014 which claimspriority to and the benefit of Italian Application No. MI2013A000216filed on Feb. 15, 2013, the content of which are incorporated byreference in their entireties.

BACKGROUND OF THE INVENTION

The present invention refers to a high-pressure mixing apparatus forpolymeric components for a reactive chemical mixture of a polymerisableresin, and more properly refers to a method for providing aself-regenerating seal in the mixing chamber of the mixing apparatus, inwhich a recirculation valving member for the polymeric componentsslides.

PRIOR ART

The high-pressure mixing apparatuses for polymeric components that aresuitable to provide reactive chemical mixtures for polymerisable resins,have been developed in various ways over time; a self-cleaninghigh-pressure mixing apparatus, usually comprises at least one mixingchamber in which two or more polymeric components are impinging withgreat kinetic energy to form a reactive mixture, and in which theresulting reactive mixture outcoming the mixing chamber flows into adelivering conduit to be injected or fed into a mould.

The mixing apparatus further comprises a sliding valve member or spoolslidable in the mixing chamber, which is provided with longitudinalgrooves for the recirculation of the single chemical components in theclosed condition of the apparatus; the sliding valve member is axiallymovable between a retracted position, in which both injection holes forthe chemical components and the mixing chamber open to the deliveringconduit, and an advanced position for recirculation of the singlepolymeric components, in which closes the mixing chamber, expelling theresidual mixture directly into the delivering conduit.

The residual mixture is in turn ejected from the delivering conduit by acleaning member, consisting of a cylindrical pin that closes the frontside of the valve member and of the mixing chamber, preventing thechemical components from leaking outwards.

The role of the delivering conduit is normally to reduce the turbulenceof the mixture and, for this reason, it is advisable that it is as longas possible; a mixing apparatus of the mentioned type is for exampledisclosed in U.S. Pat. No. 4,332,335.

In apparatuses of this type the reacted mixture tends, however, to stickthe cleaning pin to the inner surface of the delivering conduit. Theconduit length cannot therefore exceed about 6 to 7 times the diameterof the conduit; otherwise, the sticking forces would give rise to greatstresses, to excessive fatigue and gripping during sliding and removalmotion for the reacted layer of resin that has been adhered to theopposite walls of the cleaning pin and of the delivering conduit.

In order to overcome this problem, it is possible to use a cleaningmember configured with a short front head suitable for expelling thefoam, which thus sticks to a limited surface of the delivering conduit,connected to the piston of a hydraulic control cylinder by a stem ofreduced diameter.

In order to avoid, during recirculation of the chemical components withthe cleaning member in the advanced closed position, that the singlechemical components can leak into the portion of the delivering conduitwhere the stem of reduced diameter of the cleaning member extends, onthe sliding valve member one or more annular sealing elements arenormally arranged and housed in circular seats, that in the advancedcondition of the sliding valve member prevent the polymeric chemicalcomponents from leaking into the delivering conduit where, in use, theycan accumulate to form agglomerates that prevent a correct slidingthereof and tend to escape outside, polluting the reacting mixture thathas been delivered into a mould.

High-pressure mixing apparatuses are disclosed, for example, in U.S.Pat. No. 4,332,335, DE 8915329, U.S. Pat. No. 5,785,422 and EP 1927448.

In particular, U.S. Pat. No. 5,785,422 and EP 1927448 illustrate ahigh-pressure mixing apparatus, having an “L” shaped mixing chamber anddelivering conduit, in which the self-cleaning member of the deliveringconduit, as previously mentioned, comprises a piston head ofcomparatively reduced length with respect to the delivering conduit, atthe front end of a long stem operatively connected to a hydraulicactuator. The stem has a smaller diameter than the piston head and theinternal diameter of the delivering conduit; between the stem and theinternal surface of the delivering conduit, in the closed condition ofthe apparatus, an annular space is provided that substantially reducesthe contact and sticking surfaces.

Nevertheless, with this conformation of the cleaning member for thedelivering conduit, in the closed condition of the apparatus it isnecessary to prevent that the single reactive chemical components leakfrom the sliding valve member, as by entering and reacting into theannular space of the delivering conduit, they would form particles ofreacted material that would hinder the correct sliding of the cleaningmember, until to block the movement thereof if the accumulation ofreacted particles is trapped, or tend to exit outside, polluting thereactive mixture that has been delivered into a mould.

In order to prevent the polymeric components, with the mixing chamber ina closed condition, can leak through the small clearance existingbetween the sliding valve member and the inner wall of the mixingchamber, in general it has been proposed to provide the sliding valvemember with suitable annular seals.

However, by using simple annular seals on the sliding valve member,provided by a reacted resin, has not in fact solved the problem because,owing to the reciprocating movement of the valve member between theclosed and the open condition of the mixing chamber, the annular sealsslide along the front side and the corners of the holes for injectionand recirculation of the polymeric components; consequently, these sealstend to wear out rapidly. In conventional mixing apparatuses it is thusnecessary to stop repeatedly and frequently, with long productiondowntime, because of the cleaning and maintenance work that is necessaryto replace and/or restore the worn seals.

In U.S. Pat. No. 3,799,199 has been suggested to configure the slidingvalve member of the mixing chamber, with cross grooves that intersect aplurality of longitudinal grooves opening towards the mixing chamber, toenable the reactive mixture to flow back and polymerize, providingsealing ribs that longitudinally and transversely extend.

This solution is not completely suitable because during therecirculation step of the reactive components, the sliding valve memberis in a closed position and a pressure builds up in the recirculationgrooves resulting from the sum of the pressure existing in the storagetanks for the chemical components, plus the pressure drop to allow eachcomponent to flow in the respective circulation ducts and members.

In general, the pressure drop is proportional to the viscosity and tothe flowrate of the resin of the single chemical component; thus thepressure drop is greater the greater the viscosity of the singlecomponent, with a same flowrate and pipe diameter.

The flowrates are normally comparable and vary from 1.6/1 to 1/3 betweena less viscous and a more viscous component, whilst the ratio betweenthe viscosities of each component varies from 3.5 to 20, depending onapplications.

In the recirculation grooves of the valving member, pressures up to 40,50 bars can raise during recirculation, which can be unbalanced betweenone another up to 20 bars.

These pressure differences mean that between the recirculation groovesand the delivering conduit, on the damaged sides of the sealing ribs, aleak of the separate chemical components could occur, thus preventingthe regeneration of the seal.

Whilst the recirculation grooves are washed by the recirculating flow ofthe chemical components, the leaking components meet in the deliveringconduit, react with one another, or with the humidity of the air,forming encrustations that make the operation of the mixing apparatusdeteriorate.

During mixing, on the other hand, the pressure in the mixing chamber isvery small, normally lower the pressure in the longitudinal grooves ofthe sliding valve member, for which reason in U.S. Pat. No. 3,799,199the reactive mixture cannot flow back and restore the worn parts of theseals.

OBJECTS OF THE INVENTION

The main object of the present invention is to provide a method forself-regenerating seals in a high-pressure mixing apparatus of thepreviously mentioned type, in which the problem of the seal between themixing chamber and the sliding valve member, consequently the wearproblem of the seals, has been differently addressed and solved.

A further object of the invention is to provide a method, as disclosedabove, and a high-pressure mixing apparatus, for example of the typedisclosed in U.S. Pat. No. 5,785,422 or EP 1927448, in which theproblems relating to the wear of the seal of the mixing chamber, and theleakage problem of the polymeric chemical components have beenpractically eliminated.

A still further object of the invention is to provide a method and ahigh-pressure mixing apparatus, in which the seal between the slidingvalve and the mixing chamber is continuously regenerated automatically,during use, substantially reducing the time and the number ofmaintenance interventions.

SHORT DESCRIPTION OF THE INVENTION

The objects mentioned above are achievable by a method according toclaim 1 and by a high-pressure mixing apparatus according to claim 7.The solution to the problem essentially consists in providing at leastone annular sealing element of a polymeric resin, housed in a circularseat on an inner surface of a mixing chamber downstream the injectionholes for the chemical components, while worn and/or torn parts of thesealing element are automatically regenerated by the same reactivemixture that polymerizes into the worn and/or torn parts of the sealingelement during delivering of the reactive mixture and operation of themixing apparatus.

According to the invention, a method has thus been provided for forminga self-regenerating seal into a mixing chamber of a high pressure mixingapparatus, comprising the steps of:

feeding a first and at least a second polymeric component to the mixingchamber through injection holes, to form a reactive polymeric mixture,to be dispensed by a delivery conduit, in which a slidable valve memberis reciprocable in the mixing chamber between a retracted position, andan advanced position to open and respectively to close the injectionholes and the mixing chamber in respect to the delivery conduit;

providing at least one circular seat for housing an annular sealingelement on an inner surface of the mixing chamber in a sealing zonedownstream of the injection holes;

providing an annular sealing element in said at least one housing seatby a polymerisable resin; and

automatically regenerating worn and/or torn parts of the annular sealingelement, by allowing the reactive mixture to fill up and polymerize intothe worn and/or torn parts of the sealing element, inside the housingseat.

According to the invention a high-pressure mixing apparatus has beenalso provided suitable for forming a self-regenerating seal a polymericmixture of a first and at least a second reactive polymeric componentaccording to the method referred to above, the apparatus comprising:

a body portion provided with at least a cylindrical mixing chamberhaving injection holes for the reactive components opening onto an innersurface of the mixing chamber;

a delivery conduit for dispensing the polymeric mixture, the deliveryconduit transversely extending to and being in communication with anoutlet side of the mixing chamber;

a valve member slidably reciprocable in the cylindrical mixing chamber;and

at least one annular sealing element between the valve member and themixing chamber, said annular sealing element being housed in a circularseat, provided on the inner surface of the mixing chamber, in a sealingzone between the outlet side of the mixing chamber and the injectionholes.

Preferably, the delivering conduit consists of a bush removably housedin a cylindrical seat of the body of the mixing apparatus.

According to a preferred embodiment, the mixing apparatus is of the typecomprising a cleaning member for the delivering conduit provided with apiston head at the front end of a stem having a comparatively reduceddiameter that extends coaxially with the delivering bush, and isconnected to a hydraulic control actuator.

SHORT DESCRIPTION OF DRAWINGS

These and further features of the method and of the apparatus accordingto the present invention will be clearer from the description thatfollows and from the attached drawings relating to certain preferredembodiments, in which:

FIG. 1 an enlarged detail of the mixing chamber of a high-pressuremixing apparatus of conventional type, with the sliding valve member inan advanced position;

FIG. 2 is the same detail of FIG. 1 with the sliding valve member in aretracted position;

FIG. 3 is a detail similar to FIG. 2 for a high-pressure mixingapparatus, according to the invention;

FIG. 4 is a longitudinal sectional view of another embodiment of ahigh-pressure mixing apparatus, according to the invention;

FIG. 5 is a cross sectional view according to line 5-5 of FIG. 4;

FIG. 6 is an enlarged detail of FIG. 5;

FIG. 7 is a further enlarged detail of FIG. 6, showing the seat with theinitial annular sealing element;

FIG. 8 is a detail similar to FIG. 7 showing the worn andself-regenerated annular sealing element;

FIG. 9 is a longitudinal sectional view of a further embodiment of ahigh-pressure mixing apparatus, according to the invention;

FIG. 10 is a detail of a first version of the annular seal element ofthe embodiment illustrated in FIGS. 5 to 8;

FIGS. 11-14 show enlarged details of other embodiments of the annularsealing element of the embodiment illustrated in FIGS. 5 to 8;

FIG. 15 is a sectional view of the bush of FIG. 4, that shows a furtherembodiment of the annular sealing element;

FIG. 16 is an enlarged detail of FIG. 15, before the formation of theannular sealing element;

FIG. 17 is a similar detail to that of FIG. 16, after the formation ofthe annular sealing element.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show, by way of example, the detail of the mixing chamberof a high-pressure mixing apparatus of conventional type, belonging tothe prior art preceding the present invention.

In FIG. 1, with the reference number 10 the body portion of the mixingapparatus has been indicated, in which a hole has been provided defininga mixing chamber 11 in which reciprocates a sliding valve member 13 forcontrolling the flows of the chemical components to be mixed slides,which is also suitable for performing the function of cleaning memberfor the chamber 11; the mixing chamber 11 communicates with a deliveryconduit 12 for dispensing a reactive mixture, for example a polyurethanemixture obtained from a first and from at least a second polymericcomponent, such as a polyole and an isocyanate, in which the conduit 12is oriented in an orthogonal direction, transversely to the mixingchamber 11.

On two opposite sides of the mixing chamber 11 openings 14C of theinjectors 14A, 14B are provided for the supply of respective polymericcomponents A and B that are suitable for forming a reactive mixture, forexample a polyurethane mixture for the production of rigid or flexiblefoams; with 15A and 15B the recirculation openings for the singlecomponents have been further indicated, in a manner that is per seknown.

Inside the mixing chamber 11 the valve member 13 slides, which isoperatively connected to a hydraulic control actuator, which is notshown. The sliding valve member 13 is provided with two longitudinalslots 16A and 16B having a length equal to or greater than the spacebetween the axis of each injector 14A, 14B and the axis of therespective opening 15A, 15B for the recirculation of the singlepolymeric components A, B, in the closed condition of the apparatus.

Still with reference to FIGS. 1 and 2, the front end of the valve member13 has an annular seal element 17 to prevent in the advanced conditionof FIG. 1, in which the mixing chamber 11 closes towards the deliveringconduit 12, the single polymeric components A and B being able to leaktowards the delivering conduit 12 whilst they are recirculated to theopenings 15A and 15B and to respective storage tanks.

In conventional mixing apparatuses, the seal 17, which can be formed bya reactive resin, is normally housed in a seat obtained at the front endof the valve member 13; thus, at each axial movement of the valve member13, the seal 17, sliding along the mixing chamber 11, passes repeatedlyin front of the openings 14C of the nozzles 14A and 14B; consequentlythe seal rubs against the corners of these openings 14C, wearing downand becoming lacerated after a certain amount of time, at the end ofwhich the mixing apparatus has to be removed and dismantled for thenecessary maintenance operations and replacement of the worn seals.

This drawback is eliminated by the method and the high-pressure mixingapparatus according to the present invention.

With reference to FIG. 3, the innovative features of theself-regenerating seal according to the invention will now be described,with reference to a conventional mixing apparatus; in FIG. 3 the samereference numbers of FIGS. 1 and 2 have been used to indicate similar orequivalent parts.

By comparing FIG. 3 with FIG. 2, the annular seal element 17 for themixing chamber 11 has now been housed in a circular slot 17′, providedon the internal surface of the mixing chamber 11, in a seal zonedownstream of the injection holes 14C for the polymeric components, nearthe outlet opening 11′, and more properly in a seal zone comprisedbetween said outlet 11′ and the injection holes 14C. For greaterclarity, it is pointed out that the seal zone of the mixing chamber 11,in which the seal gasket 17 is positioned, substantially has tocorrespond to the cylindrical front portion 13′ of the valve member 13,comprised between the front end of the valve member 13 and therecirculation slots 16A, 16B, in the advanced condition of the valvemember in which closes the mixing chamber.

As previously mentioned, the high-pressure mixing apparatus can be ofany type and shape; a preferred embodiment thereof is represented, byway of example, in FIGS. 4 and 5 of the drawings.

As shown in the aforesaid figures, in which the same reference numbersas for the preceding figures have again been used to indicate similar orequivalent parts, the mixing apparatus again comprises a body 10 inwhich a cylindrical bore is obtained defining the mixing chamber 11, inwhich the holes 14C for the injectors 14A, 14B and the recirculationholes 15A, 15B of the single polymeric components A, B, open.

Also in this case, in the mixing chamber 11 slide a first cleaningmember consisting of a valve member 13 configured with longitudinalslots 16A, 16B; the valve member 13 is in turn operatively connected tothe piston 20 of a hydraulic actuator 21.

The mixing chamber 11 communicates with a delivering conduit 12 arrangedorthogonally to the chamber 11, in which a second cleaning member slide,consisting, in the specific case, of a pin member configured with ashort front cylindrical head 22, having a length comparatively reducedwith respect to the conduit 12, and a diameter of a few hundredths of amillimeter less than the diameter of the conduit 12. The head 22 of thecleaning member is connected to a control stem 23 having a comparativelylesser diameter, in turn connected to the stem 24 of the piston 25 of asecond hydraulic actuator 26; the hydraulic actuator 26 in turn isremovably fixed to the body 10 of the mixing apparatus, by a hollowspacer 27 having side openings 28.

The mixing apparatus according to the present invention differs fromconventional mixing apparatuses by the different conformation of thedelivery conduit 12 and of the seal between the cleaning member 13 andthe mixing chamber 11.

According to the embodiment of FIGS. 4 and 5 the conduit 12 fordelivering the reactive mixture is provided longitudinally into a bush30, which extends orthogonally to the mixing chamber 11; the bush 30 isremovably housed in a cylindrical seat of the body 10, protruding beyondthe body 10; the rear end of the bush 30 has a widened head 29 into anopposite seat of the body 10 and is retained by the spacer 27, which isremovably fixed to the body 10. Also the bush 30 with the deliveringconduit 12 is thus fastened to the body and is removable simply bysliding; thus, after removing the spacer 27 with the actuator 26, it ispossible to remove both the bush 30 and the second cleaning member 22,23 for the necessary maintenance operations, or to replace them with anew bush and/or with a new cleaning member 22, 23 of the same type or ofa different type.

From FIG. 4 it is further shown that the stem 23 of reduced diameterextends at the rear from the head 22 along the hole of the deliveringconduit 12; thus, between the stem 23 and the internal surface of thedelivering conduit 12, in the advanced condition, an annular space 31 isformed that opens at the rear to the hollow spacer 27, to the exterior.

This solution of the cleaning member 22, 23, in combination with theself-regenerating seal of the mixing chamber 11, enables the performanceof the mixing apparatus to be improved further.

In order to ensure a laminar flow of the mixture jet that exits thedelivering conduit 12, and to enable the same conduit 12 to enter thecavities of the foaming member, it is desirable for the conduit 12 andthe bush 30 to be as long as possible. Currently, conduits 12 are usedwhich are 5 to 6 times longer than the diameter; for certainapplications, the conduit 12 has to be 10 to 15 times the diameterthereof.

In these conditions, if the cleaning member of the delivering conduit 12were totally cylindrical, of a constant diameter and of significantlength, it would sealingly close the end of the mixing chamber at thefront of the valve member; nevertheless, an excessive length of thecleaning member of the delivering conduit 12, would create openingproblems, because of the sticking between contact surfaces caused by thereacted polymer, and overheating during the repeated reciprocalmovements.

For these reasons, it is advisable to use a cleaning member providedwith a short piston head 22, as shown in FIG. 4.

Nevertheless, with a cleaning member provided with a piston head, theresins that leak from the valve member in the closed position, arepushed outwards, polluting the product; or the resins that form thereactive components A, B, penetrating the annular space of thedelivering conduit 12, would be scraped towards the spacer 27 where theywould accumulate as a sticking residue, also including residues ofreacted material, in this manner the good operation of the apparatuswould be compromised.

If the cleaning member of the conduit 12 were maintained in theretracted open position, the resins that exit seeping from the valvemember in the closed position would drip through the delivering conduit,onto the piece damaging the same piece.

For these reasons, and for the purposes of the present invention, in theadvanced closed condition of the valve member 13 and if the deliveringconduit 12 is kept clean by a sliding element configured with differentdiameters, it is indispensable to ensure a good seal between the mixingchamber 11 and the delivering conduit 12.

With reference to FIGS. 4-8, the innovative features of the apparatusand of the method for self-generating a seal between the valve member 13and the mixing chamber 11 will be now disclosed in greater detail.

From the various figures it is in fact noted that the bush 30, in anintermediate position, has a cross hole 32 that is axially aligned tothe mixing chamber 11, constituting in the specific case an extension ofthe same mixing chamber; the cross hole 32 is thus configured with acylindrical internal surface 33 (FIGS. 7 and 8) consisting of anextension of the cylindrical internal surface 11.1 (FIGS. 6 and 7) ofthe mixing chamber 11, which is open to the delivery conduit 12.

In the internal surface 33 of the cross hole 32 of the bush 30, at leastone circular slot or seat 34 has thus been obtained in which an annularsealing element 35 is housed for the necessary seal between the mixingchamber 11 and the valve member, in respect to the delivery conduit 12,in the totally advanced condition of the valve member 13 in which closesthe mixing chamber 11; in the case shown, the circular housing seat 34has a rectangular a cross section, but other forms of the housing seatand of the sealing element are possible, as explained below.

The annular sealing element 35 can be formed in various ways; forexample can be initially obtained by spreading into the housing seat 34,and filling the housing seat 34 with any synthetic resin that suitablefor the purpose, with a possible filler and polymerised afterapplication; the excess of solidified material is then removed, leavinga slight swelling towards the inside, as shown in FIG. 7. Alternatively,the annular sealing element 35 can be provided by the same reactivemixture that initially fills and polymerizes in the housing seat 34.

In the embodiment of FIG. 7, the housing seat 34 is “closed” to bothsides of the bush 30, whereas it is radially “open” to the inside of thecross hole 32; nevertheless, as shown in the remaining embodiments, thehousing seat 34 at one or both sides could be opened inside and outsidethe bush 30; in this case the seal element 35 would also seal thecontact zone 30.1 consisting of the interface between the bush 30 andthe body 10 of the mixing apparatus; nevertheless, it is necessary toform the annular seal element with protuberances or with continuousand/or discontinuous circular beads that engage in corresponding seatsof the cross hole of the bush 30, to retain the seal element, or toprevent a possible axial running of the resin that is dragged by thevalve member.

According to the embodiment under consideration, having formed theinitial annular seal element 35 in a housing slot or seat 34 inside thecross hole 32 of the bush 30, in replacement of the usual annular sealelement normally provided on the valve spool 13, permits numerousadvantages, both from the constructional and functional point of view.

From the constructional point of view it is clear that as the bush 30 isseparate and removable from the body 10 of the apparatus, it is easierto operate to initially form the annular seal element 35, beforeassembling the mixing apparatus. This operation can also be performedsubsequently by removing in an extremely easy manner the bush 30 whennecessary, during a maintenance operation, or when a bush has to bereplaced with another one of a different type, or to replace it when thebush is worn.

Providing the annular seal element 35 in the housing seat 34 of thecross hole 32 of the bush 30, or more in general near the outlet openingof the mixing chamber 11, also brings certain functional advantages.

This can be explained more fully with reference to FIGS. 7 and 8; FIG. 7shows the original annular seal element 35, whole and devoid of wornparts or form parts. Nevertheless, the valve member 13, throughrepeatedly reciprocating movement at each opening and closing of themixing apparatus, tends to wear down or torn over time the seal element35, removing part of the original resin, as shown in FIG. 8; in thismanner the seal would be compromised.

Nevertheless, according to the present invention, having positioned theannular seal element 35 no longer on the valve member 13 of the mixingchamber 11, but into the cross hole 32 of the bush 30 of the deliveringconduit, or more in general in a housing seat provided on the innersurface of the mixing chamber 11, as previously mentioned, permitsself-generation of the seal by the same reactive mixture; in fact, ateach delivering or dispensing slot, the reactive mixture outcoming fromthe mixing chamber 11 flows to the delivery conduit 12, fills andpolymerizes in the cavities or in the worn parts, or lacerations in thesealing element 35; this has been clearly shown with the referencenumber 36 in FIG. 8. The sealing member 35 can be continuallyregenerated, extending in this manner the working life of the mixingapparatus.

FIG. 9 shows a second embodiment of a high-pressure mixing apparatusprovided with a self-regenerating seal according to the presentinvention; the mixing apparatus of FIG. 9 differs from the apparatusillustrated in FIGS. 4 to 8 by in that the conduit 12 for delivering themixture is now formed in an external bush 30′, axially aligned to acylindrical hole 12A, of the same diameter, directly provided in thebody 10 of the mixing apparatus, orthogonally to the mixing chamber 11;other solutions are nevertheless possible in terms of features of themixing apparatus, the use of a self-regenerating seal according to thepresent invention remaining unchanged.

In particular FIG. 9, similarly to FIG. 3, shows an annular sealingelement 35 in a housing seat 37 on the internal surface of the mixingchamber 11, at the outlet end 39 that communicates with the deliveryconduit 12, 12A. The annular sealing element 35 performs the samefunction as the annular sealing element 35 of the example of FIGS. 4-8and is made in a manner completely similar to the latter, i.e. coatingand filling the housing seat 34 with a synthetic resin, i.e. enablingthe reactive mixture to fill the housing seat 34 subsequently, leavingthe reactive mixture to polymerize.

Also this second embodiment of the invention has the advantage that theannular sealing element 35, similarly to the annular sealing elementpreviously disclosed, is self-regenerated during use by the reactivemixture dispensed by the apparatus.

FIGS. 10 to 14 show further variants and further features of theself-regenerating seal according to the present invention.

Whilst in the case of FIGS. 4-8 the annular sealing element 35 is housedin a seat 34 provided on the inner surface 33 of the cross-hole 32 ofthe bush 30, in which the seat 34 consists of an annular groove closedon both sides as shown in FIG. 8, the seal 34 being on the other handopen radially to the inside of the mixing chamber 11 so that the sealcontact occurs between the internal surface of the sealing element 35and the cylindrical surface of the valve member 13, in the case of FIG.10 the cross hole 32 of the bush 30, which constitutes an extension ofthe front end of the mixing chamber 11, is configured with an annularhousing seat that is open both radially towards the cross hole 32 and onone side towards the interface 30.1 between the outer surface of thebush 30 and a mating surface of the body 10; in this manner the annularsealing element 40 is allowed to be extended as far as the contactinterface 30.1. A dual seal is thus obtained, both towards the valvemember 13 of the mixing chamber 10, and between the bush 30 and the body10 of the apparatus, by means of an annular sealing element 40 having arectangular cross-sectional shape.

The solution of FIG. 11 differs from the solution of FIG. 10 by thedifferent shape of the annular sealing element 40 and of the circularhousing slot or seat 41 in the cross hole 32 of the bush 30, thus alwayspermitting a dual seal as in the preceding case.

According to the example in FIG. 11 the annular sealing element 40comprises a first cylindrical part 42, having inner and outercylindrical surfaces and a cross section with a substantially constantthickness, that extends as far as the contact interface 30.1 between thebush 30 and the body 10, and an annular ridge 43, having a circularcross-sectional shape, housed in a corresponding seat in the bush 30 toretain the annular sealing element 40.

Again, the fact that the housing seat and the annular sealing element 40housed therein extend as far as the interface 30.1 provided by thecontact zone between the bush 30 and the body portion 10, improves theseal between the mixing chamber 11 and the delivering conduit 12, in thetotally advanced condition of the valve member 13.

FIG. 12 illustrates a further version; in this case the annular sealingelement 40 has again a first cylindrical part 42, still bounded bycylindrical surfaces, which extends as far as the interface 30.1, and anannular ridge 43 having a conical outer face and a triangular crosssectional shape, housed in a correspondingly shaped seat for retainingthe sealing element 40 in both the axial directions.

FIG. 13 illustrates a further version of the annular sealing element 40that always consists of a first cylindrical part 42 having a crosssectional shape of substantially constant width, and a second part 43 inthe shape of a ridge configured with opposite conical outer surfaces.

FIG. 14 shows a further solution for the annular sealing element 40, andthe sealing seat, has a first cylindrical part 42 that extends towardsthe interface 30.1, and a second cylindrical part 43, of greaterdiameter, housed in a suitable seat for anchoring the annular sealingelement 40 to the bush 30, and for again preventing the annular sealelement 40 from being dragged and removed by the valve member duringaxial movement thereof.

FIGS. 15 to 17 show a further version of the housing seat and theannular sealing element 40; the solution of FIGS. 15-17 is particularlysuitable if the bush 30 is of small diameter or has a cylindrical wallof reduced thickness compared to previous solutions; again in FIGS.15-17 the same reference numbers as in the previous figures have beenused to indicate similar or equivalent parts.

In this case the housing seat for the annular sealing element 40 isconfigured by a cross hole of the bush 30, having a greater diameterthan the mixing chamber 11; as shown in FIG. 17, the sealing element 40extends on both outer sides of the bush 30, both towards the deliveringconduit 12 and towards the contact interface 30.1 between bush 30 andbody 10 of the apparatus. In the case of FIGS. 15 to 17, as shown in thedetail of FIG. 16, to anchor the annular sealing element 40 to the bush30, arch-shaped grooves 45 are provided in the latter, into which theresin can penetrate, forming corresponding anchoring toothings 46 shownin FIG. 17; in all cases, the toothings 46 prevent the resin frompossibly running when dragged by the valve member 13.

The angular extent, the thickness and depth of the arch-shaped grooves45, can vary according to the needs and dimensions of the bush 30. Inthe case shown, the grooves 45 have a depth that gradually decreases oneend to the other end; other forms of grooves 45 are of course possible.

According to the invention, a method has thus provided for forming aself-regenerating seal, in a high-pressure mixing apparatus forchemically reactive polymeric components, for example for formingpolyurethane mixtures, in which the apparatus comprises at least onemixing chamber 11 and a valve member 13 that is made axially reciprocatebetween an advanced closing condition for the mixing chamber 11, and aretracted opening position in which the mixing chamber 11 communicateswith a delivering conduit 12 for the reactive mixture, which extendsorthogonally to the mixing chamber 11, according to which:

at least one circular seat 34, 41 for housing a sealing element isformed in the internal cylindrical surface of the mixing chamber 11, oron an extension thereof, at a sealing zone towards the deliveringconduit 12, downstream injection holes for the chemical components;

forming an annular sealing element 17, 35, into the seat 34, 41 byspreading a polymerisable resin and filling the housing seat with thepolymerisable resin or with the same reactive mixture; andself-generating worn and/or torn parts of the annular seal elementduring the operation of the mixing apparatus, with the same reactivemixture that is left to polymerize in the worn and/or torn parts orcavities of the annular seal element thus restoring its continuity.

Comparative tests have been conducted between a conventional mixingapparatus, provided with a sealing element on the valve member of themixing chamber, and a mixing apparatus according to the presentinvention; from the tests it has been established that in a conventionalapparatus the seal wore out early, so that it was necessary to replacethe sealing member after a relatively small number of disworking cycles,on average 50,000 working cycles. On the other hand, by positioning theannular sealing element in a housing seat provided inside the mixingchamber or an extension thereof, according to the previously illustratedembodiments, the useful working life of the mixing apparatus wassignificantly extended; in this case it was established that after400,000 working cycles it was not necessary to intervene to reconstructthe sealing element 35, 40, with an increase of the useful life of theseal and a consequent increase of productivity.

From what has been said and shown in the embodiment of the attacheddrawings, it is thus clear that a method and a high-pressure mixingapparatus for chemically reactive polymeric components have beenprovided, for example for the production of both flexible and rigidpolyurethane foams, characterized by a seal between mixing chamber anddelivering conduit that self-generates continuously with the samereactive mixture dispensed during normal operation of the apparatus. Itis thus understood that other modifications or variations can be made tothe apparatus or the parts thereof without thereby departing the claims.

What we claim is:
 1. A high pressure mixing apparatus suitable forforming a self-regenerating seal by a polymeric mixture of a first andat least a second reactive polymeric components, the apparatuscomprising: at least a cylindrical mixing chamber having injection holesfor the reactive components opening onto an inner surface of the mixingchamber; a delivery conduit for dispensing the polymeric mixture, thedelivery conduit transversely extending to and being in communicationwith an outlet side of the mixing chamber; a valve member slidablyreciprocable in the cylindrical mixing chamber; and at least one annularsealing element between the valve member and the mixing chamber, saidannular sealing element being housed in an annular housing seat,provided on the inner surface of the mixing chamber, in a sealing zonebetween the outlet side of the mixing chamber and the injection holes.2. The high pressure mixing apparatus according to claim 1, in which thedelivery conduit consists of a bush comprising a cross hole axiallyaligned to the mixing chamber, in which the annular housing seat forhousing the annular sealing element is provided on an internal surfaceof the cross hole.
 3. The high pressure mixing apparatus according toclaim 2, in which the annular housing seat has at least one open side,said annular sealing element extending to said open side of the annularhousing seat and to a contact interface between an outer surface of thebush and a facing surface of the body portion of the mixing apparatus.4. The high pressure mixing apparatus according to claim 1, in which theannular sealing element is provided with at least one protrusionengaging into a shaped cavity of the annular housing seat, having across section selected from: circular, semicircular, triangular,rectangular or combination thereof.
 5. The high pressure mixingapparatus according to claim 2, wherein the bush is removably seated andprotrudes from the body portion of the mixing apparatus.
 6. The highpressure mixing apparatus according to claim 1, comprising areciprocable cleaning member for the delivery conduit having a forecylindrical head and a rear stem of comparatively reduced diameter,operatively connected to a linear actuator.